bullets.py

import pygame
from pygame.sprite import Sprite

class Bullet(Sprite):
    #manages bullets fired from the ship
    '''sprites enables us to group related elements in the game'''
    def __init__(self,ai_settings,screen,ship):
        super(Bullet,self).__init__()
        #inherits the ai_settings,screen and ship attributes from Sprite using super
        self.screen = screen
        #creates a bulet rect at (0,0) and sets its correct position
        self.rect = pygame.Rect(0,0,ai_settings.bullet_width,ai_settings.bullet_height)
        self.rect.centerx = ship.rect.centerx
        self.rect.top = ship.rect.top
        #stores bullets position as a decimal value
        self.y = float(self.rect.y)

        self.color =ai_settings.bullet_color
        self.speed_factor =ai_settings.bullet_speed_factor
    def update(self):
        #updates the decimal position of the bullet
        self.y -=self.speed_factor
        self.rect.y = self.y

    def draw_bullet(self):
        #displays bullets on the screen
        pygame.draw.rect(self.screen,self.color,self.rect)